It is known that a combination of a p-type conducting organic polymer as a cathode and a metal having a lower redox potential than that of the polymer as an anode can provide a secondary battery capable of charging and discharging as described, e.g., in U.S. Pat. No. 4,442,187, D. MacInnes et al., J. Chem. Soc., Chem. Commun., 317 (1981), A. G. MacDiarmid et al., J. Electrochem. Soc., Vol. 128, 1651 (1981), and JP-A-No. 61-200669 (the term "JP-A" as used herein means "unexamined published Japanese patent application").
p-Type conducting organic polymers which have conventionally been used in the above-described secondary batteries are polymers that are cationic by themselves and are doped with a low molecular weight anion, such as perchlorate, chlorine and tetrafluoroborate ions. On reduction in an electrolyte solution, they become neutral by releasing the anion and, on reoxidation, capture again the anion as a dopant. In other words, the p-type conducting organic polymers having a low molecular weight anion as a dopant have a reversible anion-incorporating ability.
On the other hand, the metal to be used as an anode becomes a metal ion upon oxidation in an electrolyte solution and the metal ion is dissolved in the electrolyte solution. On re-reduction, the metal ion is precipitated as a metal.
FIGS. 4A and 4B illustrate a conventional battery in which cathode 41 comprises the above-described conducting organic polymer which is cationic and is doped with a low molecular weight anion and anode 43 comprises a metal. In the conventional battery, during discharge, anion X.sup.- is released from the cathode and cation M.sup.+ (metal ion) is dissolved from the anode, whereby the ion concentration in the electrolyte solution 46 considerably increases. On the other hand, these reactions are reversed during charging. That is, anion X.sup.- is incorporated by the cathode and metal ion M.sup.+ precipitates as a metal on the anode, whereby the ion concentration in the electrolyte solution 46 markedly decreases. It is therefore apparent that the charging and discharging characteristics of batteries of this type depend on diffusion of both the metal ion and the anion.
In these conventional batteries, it is necessary to use an unsaturated electrolyte solution in excess relative to the volume of the conducting organic polymer and the metal as the electrode active materials, from considerations that the ions released from both cathode and anode on discharging should be dissolved in the electrolyte solution and that the internal resistance of the battery should be reduced by maintaining a sufficient ion concentration of the electrolyte solution during charging. Therefore, although the batteries have a relatively high energy density as calculated from only the weight of the electrode active materials, they have a seriously poor energy density when taking the weight of the electrolyte solution into consideration, which has been a serious problem to their practical application.
The inventors previously proposed p-type conducting organic polymers doped with a high molecular weight polymer having a number of anionic groups in the molecule thereof (hereinafter referred to as a "polymer anion") in place of the above-described low molecular weight anion, as reported in Ohtani et al., Polymer Preprints Jpn. No. 34, 2829 (1985). In marked contrast to the p-type conducting organic polymer doped with a low molecular weight anion, since the polymer anion as a dopant is hardly diffusible in the conducting organic polymer because of its high molecular weight, the conducting organic polymer incorporates a cation in the electrolyte solution within its molecule by reduction of the conducting organic polymer in the electrolyte solution and then releases the cation thus incorporated upon re-oxidation of the conducting organic polymer. That is, the p-type conducting organic polymer doped with the polymer anion possesses a reversible cation-incorporating ability.
There has also been proposed a plastic battery containing the above-described conducting organic polymer doped with a low molecular weight anion as a cathode and a conducting organic polymer doped with the above-described polymer anion as an anode as disclosed in Japanese Patent Application No. 61-214816. This type of battery also requires an electrolyte solution in excess.